The Queensland state Premier Anastasia Palaszczuk told reporters in Townsville that the area was in "unprecedented times", with the city recording over one metre (3.2 feet) of rainfall in the past seven days.
Up to 500 homes have been flooded and the Bureau of Meteorology (BoM) warned of more rain over the area and over the city's swollen Ross River Dam, local media reported.
The BoM also warned of possible tornadoes forming, according to local media.
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The city's officials said about 10,000 homes were without electricity.
Rescuers also rescued people from inundated homes.
"Just that the water keeps rising and I'm very scared of water, I'm terrified of water", resident Tina Stephensen told the Australian Broadcasting Corporation (AuBC) after she was rescued in a dinghy.
Australian Defence Force personnel delivered 90-thousand sandbags to affected properties, local media reported.
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Billabong Sanctuary Ranger Kate de Koning told the AuBC that rangers were busy caring for the animals, with some being moved to staff rooms to escape the rain.
Palaszczuk said many schools in the area will remain closed on Monday.
